76 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



that the resultant phenomena could be explained entirely by 

 variations in the amount of blood, and that the nervous system 

 influences their secretion only by contraction and dilatation of the 

 vessels. However, a number of circumstances, which it is un- 

 necessary to relate here, prove that the secretory fibers exert an 

 influence directly upon the cells themselves, causing them to 

 secrete. The mere distribution of these fibers to the gland cells 

 presupposes some such function on their part ; and it can actually 

 be shown that the secretion can be increased when the blood 

 supply is cut 'off, or without dilatation of the vessels. Such 

 action, however, is of course only temporary, for the materials 

 for secretion must be supplied by the blood. The exact method 

 of termination of the secretory fibers has not been determined. 

 It is probable that they end between and around the cells and do 

 not penetrate their substance. 



Section of the chorda tympani causes a continuous flow of 

 saliva from the submaxillary and sublingual glands for several 

 weeks. This has been termed paralytic secretion, and is sup- 

 posed to be due to the fact that the chorda fibers do not them- 

 selves run directly to the glands, but are distributed to sym- 

 pathetic ganglia (the submaxillary or others in the gland sub- 

 stance). Section of the chorda, then causes, degeneration of 

 its fibers only as for as these ganglia, and their cells are thought 

 to be subject, in some obscure way, to continuous irritation 

 during the period for which the paralytic secretion continues. 



Function. The function of this secretion is twofold, (a) 

 mechanical and (b) chemical. 



(a) From a mechanical standpoint (i) it facilitates phona- 

 tion, mastication and gustation by maintaining a proper degree 

 of moisture in the mouth; (2) its more watery parts (parotid) 

 mix with the food, dissolving part of it, so that it may be more 

 easily masticated and swallowed while its more viscid parts 

 (submaxillary and sublingual) spread over the surface of the 

 bolus to aid in deglutition. 



